1. Field of the Invention
This invention relates generally to semiconductor processing, and more particularly, to a method and apparatus for determining metal chemical mechanical polishing (CMP) endpoint using integrated polishing pad electrodes.
2. Description of the Related Art
CMP is a widely used means of planarizing silicon dioxide as well as other types of processing layers on semiconductor wafers. Chemical mechanical polishing typically utilizes an abrasive slurry disbursed in an alkaline or acidic solution to planarize the surface of the wafer through a combination of mechanical and chemical action. Generally, a chemical mechanical polishing tool includes a polishing device positioned above a rotatable circular platen or table on which a polishing pad is mounted. The polishing device may include one or more rotating carrier heads to which wafers may be secured, typically through the use of vacuum pressure. In use, the platen may be rotated and an abrasive slurry may be disbursed onto the polishing pad. Once the slurry has been applied to the polishing pad, a downward force may be applied to each rotating carrier head to press the attached wafer against the polishing pad. As the wafer is pressed against the polishing pad, the surface of the wafer is mechanically and chemically polished.
As semiconductor devices are scaled down, the importance of chemical mechanical polishing to the fabrication process increases. In particular, it becomes increasingly important to control and determine endpoint for a polishing process (i.e., determining when a processing layer is sufficiently removed from a surface of a wafer.) Generally, a variety of known techniques may be used to determine endpoint for a polishing process. For example, during a polishing process, electrical current supplied to the rotating carrier heads of a polishing tool may be monitored. Moreover, because various processing layers of a wafer may have different coefficients of friction, the endpoint of a polishing process may be determined by changes in the current supplied to the rotating carrier heads. For example, depending upon the coefficient of friction of the underlying process layer or semiconductor substrate, an increase or decrease in the current supplied to the rotating carrier heads may signal the endpoint of a polishing process.
In addition to carrier current, optical sensors may be used to detect endpoint of a polishing process. For example, in one embodiment, openings may be defined in a polishing pad of a polishing tool, and a laser beam, originating from the platen, may be directed through the openings in the polishing pad and reflected off a polishing surface of a wafer. Once reflected, the phase angle of the reflected laser beam may be measured using optical sensors embedded in the platen of the polishing tool. Those skilled in the art will appreciate that the endpoint of the polishing process may be determined by a predetermined change in the phase angle of the reflected laser beam.
The existing endpoint detection techniques for wafer polishing processes, however, suffer from several shortcomings. For example, because of semiconductor process variations, such as surface non-uniformity of a wafer, existing control techniques may inadequately determine endpoint for a polishing process. Moreover, traditional endpoint techniques, such as carrier current, polishing pad temperature, etc., are based on bulk polishing action across the surface of the wafer. With these techniques, endpoint may be prematurely determined. For example, endpoint may be incorrectly signaled after removing only 90% of the process layer from the surface of the wafer resulting in residual unpolished process layer remaining on the surface of the wafer. In addition, other endpoint techniques, such as optical detection, xe2x80x9clookxe2x80x9d for endpoint based on the process layer located at the edge of the wafer. With these techniques, any residual process layer located at the center of the wafer may not be detected.
Unfortunately, the problems experienced with traditional endpoint control techniques may be exacerbated when polishing metal or other electrically conductive process layers. For example, small residual patches of metal remaining on a surface of a wafer, if not detected, may result in electrical shorts or other parametric failures in the final semiconductor devices (e.g., microprocessors, microcontrollers, memory, etc.) Moreover, such residual patches of metal or other conductive process layers, if not removed, may significantly reduce production yield, thus, increasing manufacturing costs.
The present invention is directed to overcoming, or at least reducing the effects of, one or more of the problems set forth above.
In one aspect of the present invention, a polishing system is provided. The system includes a polishing tool having a platen, a polishing pad, and a controller. The platen is adapted to have the polishing pad attached thereto. The polishing pad includes a polishing surface and a back surface that is opposite the polishing surface. At least one sender electrode and at least one response electrode is disposed in the polishing pad. The controller is coupled to the polishing tool.
In another aspect of the present invention, a method is provided. The method includes polishing a conductive process layer of a wafer using a polishing pad of a polishing tool having at least one sender electrode and at least one response electrode disposed therein. A signal is provided to the at least one sender electrode. The signal provided to the at least one sender electrode is monitored with at least one of a group of the at least one response electrode, the at least one response electrode communicating with the at least one sender electrode through the conductive process layer of the wafer. Endpoint of the polishing process is determined based on the signal received by the at least one response electrode.